1. Field of the Invention
The invention relates to a strapping machine, more particularly to a strapping machine with a strap tightening adjustment unit of a simple structure.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional strapping machine is shown to include a machine body 1, a strap supply reel 14, a strap feed unit 13, a rotating shaft unit 122, and a strap tightening adjustment unit 4.
As illustrated, the machine body 1 defines an accommodating space 11 and a package-strapping space 12 above the accommodating space 11. The strap supply reel 14 is mounted on an exterior of the machine body 1. A bundle of strap 2 is mounted on the strap supply reel 14, and has a leading end fed into the package-strapping space 12 by the strap feed unit 13 in such a manner that a package strapping operation can be done in the package-strapping space 12. The rotating shaft unit 122 is journalled in the accommodating space 11 of the machine body 1, and is formed with a cam unit 123.
The strap tightening adjustment unit 4 includes a spring-loaded swing arm 41, a clamp unit 5, and a strap tension adjuster 6. A mounting shaft 113 extends through a mounting bracket 111 of the machine body 1 and the swing arm 41 to mount the latter pivotally within the accommodating space 11. The swing arm 41 is further associated with the rotating shaft unit 122 via the cam unit 123 in such a manner that rotation of the shaft unit 122 results in turning of the swing arm 41 relative to the machine body 1 along a travelling path 131 between an upper position adjacent to the package-strapping space 12 and a lower position distal from the package-strapping space 12. The swing arm 41 defines a strap passage 414 to permit extension of the strap 2 therethrough, and a rod-path 415 in spatial communication with the strap passage 414. The clamp unit 5 includes a clamp piece 54, a push rod 51, and a torsional spring 52. The clamp piece 54 is mounted pivotally on the swing arm 41 via a pivot 53. The push rod 51 is disposed movably in the rod-path 415 of the swing arm 41, and is operably associated with the clamp piece 54. The torsional spring 52 is sleeved around the pivot 53 so as to urge the push rod 51 in the rod-path 415 toward a first direction away from the strap passage 414 so as to relieve clamping of the clamp piece 54 relative to the strap 2. The strap tension adjuster 6 includes an adjuster shaft 61 which is mounted rotatably in the mounting bracket 111 of the accommodating space 11 and which extends parallel to and adjacent to the mounting shaft 113, a spring-loaded rod pusher 64 which is sleeved on the mounting shaft 113 and which urges the push rod 51 to move in a second direction opposite to the first direction so as to result in clamping of the clamp piece 54 relative to the strap 2 in the strap passage 414, and a tension adjusting wheel 62 which is fixed eccentrically on the adjuster shaft 61 and which is in sliding contact with the rod pusher 64 via a coupler unit 63.
When the swing arm 41 is pivoted to a position between the upper and lower positions by virtue of rotation of the shaft unit 122, the rod pusher 64 and the coupler unit 63 concurrently rotate with the swing arm 41. Collision of a protrusion 631 on the coupler unit 63 with the adjusting wheel 62 results in stoppage of the rotation of the coupler unit 63 on the shaft 113, which in turn, results in movement of the clamp piece 54 in the second direction toward the strap passage 414 of the swing arm 41 by virtue of urging action of the rod pusher 64 against the push rod 51 (see FIG. 4), thereby clamping and tightening the strap 2 around the package that is disposed in the package-strapping space 12 of the machine body 1.
Note that the strap tightening adjustment unit 4 of the conventional strap machine includes a relatively large number of components, and is therefore consequently complicated in structure and incurs a long assembly time during the manufacture of the conventional strapping machine.
Therefore, the object of this invention is to provide a strapping machine with a strap tightening adjustment unit of a simple structure so as to overcome the aforementioned disadvantages that are associated with the conventional strapping machine.
Accordingly, a strapping machine of the present invention includes a machine body, a strap supply reel, a strap feed unit, a rotating shaft unit, and a strap tightening adjustment unit. The machine body defines an accommodating space and a package-strapping space above the accommodating space. The strap supply reel is mounted on the machine body, and is adapted to hold a bundle of strap thereon. The strap feed unit is capable of feeding the strap from the strap supply reel to the package-strapping space of the machine body. The rotating shaft unit is journalled in the accommodating space of the machine body, and is formed with a cam unit. The strap tightening adjustment unit includes a spring-loaded swing arm, an electrically operated clamp unit, a detecting device, and a delay circuit. The swing arm is pivoted to the machine body within the accommodating space, and is associated with the rotating shaft unit via the cam unit in such a manner that rotation of the shaft unit results in turning of the swing arm relative to the machine body between an upper position adjacent to the package-strapping space and a lower position distal from the package-strapping space. The swing arm defines a strap passage which is adapted to permit extension of the strap therethrough. The clamp unit is mounted movably on the swing arm, and is movable relative to the strap passage between a clamping position, in which the strap is clamped by the clamp unit, and a releasing position, in which the strap is released from the clamp unit. The delay circuit is electrically coupled to the detecting device and the clamp unit. When the detecting device detects a first position of the swing arm between the upper and lower positions, the delay circuit will actuate the clamp unit to move from the releasing position to the clamping position after a preset delay time. When the detecting device detects a second position of the swing arm between the first and lower positions, the clamp unit is immediately actuated to move from the clamping position to the releasing position.